This invention relates generally to golf irons and more particularly concerns a set of golf irons including long distance irons and short distance irons which set, beginning with the long irons, has progressively decreasing displacement between the center line of the hosel and the center of mass of the head. In addition each iron within the set has a support column in a cavity behind the center of mass of the head, a pattern of horizontal face grooves with parabolic sides which pattern of grooves is configured to disguise the progressive displacement, and a planar segment on the sole to cause the head to sit squarely at address.
Golf irons typically include a set of eleven irons, numbered one (long) through nine, (short) a pitching wedge, and a sand wedge. Each iron comprises a head including a hosel and a shaft which is attached to the head by fitting the shaft into the bore of the hosel. The hosel is attached to and is integral with the head. The head includes a heel, a bottom sole, a toe, a planar striking face, and a backside.
The eleven irons of a set conventionally have varying degrees of loft angle and lie angle. The loft angle of an iron is the angle between a vertical plane, which includes the shaft, and the plane of the striking face of the iron. The lie angle of an iron is the angle between the shaft and the ground (horizontal plane) when the tangent to the sole directly under the center of mass is in the horizontal plane and when the shaft lies in a vertical plane.
The loft angle, as the name suggests, determines how much loft is imparted to the ball when it is struck by the tilted striking face. The lie angle of the iron assures that, when swung properly, the sole of the iron will contact the ground evenly so that the striking face will not tend to twist inwardly or outwardly.
Although the loft and lie angles may vary slightly between different brands of iron, the loft and lie angles (in degrees) for irons generally are shown in Table 1.
TABLE 1 ______________________________________ Iron # Loft Angle Lie Angle ______________________________________ 1 16 57 2 18 57.5 3 21 58 4 24 59 5 27.5 60 6 32 60.5 7 37 61 8 41 61.5 9 45 62 Pitching Wedge 50 63 Sand Wedge 58 63 ______________________________________
For any set of golf irons, it is important that for a consistent swing, the iron impart consistent loft and distance to the ball. It is also important that when properly swung, the iron produces a consistent shot without tendency to hook or slice.
Even when conventional irons are swung consistently, such irons vary in their loft change at impact due to centrifugal forces. The prior art teaches that that tendency to change loft can be compensated for by providing a set of golf irons which have progressively decreasing offsets, beginning with the long iron (#1) and progressively decreasing toward the short irons (sand wedge). The offset is the distance between the leading edge of the face of the iron and the axis of the shaft in the horizontal direction into the striking face of the iron (Y-direction). For long irons, the leading edge of the face actually trails the axis of the shaft. For short irons, the leading edge of the face actually proceeds the axis of the shaft. The offset is related to the distance by which the center of mass of the head trails the axis of the shaft. The center of mass for short irons trails the axis of the shaft by more than the center of mass for long irons trails the axis of the shaft.
Because of the offset and the related position of the center of mass, the centrifugal forces that result about the center of mass of the head when the iron is swung tend to cause the iron to increase its loft angle as the shaft bends and to cause the head to twist about the shaft axis toward a more closed face position as the face of the iron comes into contact with the ball. By progressively varying the offset from the long irons to the short irons, an appropriate degree of consistent loft change can be achieved from iron to iron.
Offset in a conventional set of irons also tends to induce a twisting action at the head which closes the face and produces a hook. That twisting action is greater for the short irons with their larger head mass than for the long irons with their smaller head mass.
It is also well known in the art to design golf irons with the majority of the weight concentrated at the heel and toe of the iron in order to increase the moment of inertial about the center of mass of the irons so that the head will not tend to twist if the ball is struck slightly off center. Such weight distribution is generally accomplished by providing a cavity in the backside of the iron centered about the center of mass so that the remaining mass of the head of the iron is concentrated at the heel and toe. Because of the cavity in the backside of the iron, the iron has a very thin blade at the center of mass directly behind the striking face. Consequently, when a ball is struck with such a thin bladed iron, the iron produces a hollow sound which is considered objectionable by many golfers.
In a conventional set of irons each iron has a number of horizontal grooves extending across the planar striking face. The grooves provide escape channels for water so that the ball will not hydroplane up the planar striking face and thereby not take any back spin from the iron. When the striking face fails to impart back spin to the ball, the ball will flutter (like a knuckleball), will tend to fly farther than anticipated, and will not hold (bite) the playing surface upon landing. Conventionally, the grooves have either been V-shaped in cross section or have been box-shaped in cross section. In each case, the junction between the planar striking face and the sides of the grooves has been generally sharp which tends to scuff the balls as the striking face imparts spin to the ball. Also, the V-shaped groove and the box-shaped groove do not provide maximum cross sectional area for handling the volume of water that may be present between the striking face and the ball.
Conventional irons generally have a rounded convex sole. When conventional irons are grounded at address, the iron may not be properly aligned both heel to toe or face to backside. Such improper address, may effect the golfer's subsequent striking of the ball.